Laboratory research of sealing and gas-plugging drilling fluid system in fractured gas reservoir

The gas reservoirs in Shunnan Block are characterized by developed micro-fractures, and they are suffered from serious gas cut and frequent leakage in the process of well drilling. To solve these problems, the physical+chemical film plugging technology was researched. Firstly, the cores with artificial fractures (fracture aperture 0.01, 0.05 and 0.1 mm) were prepared. Then, the key plugging materials were selected by means of sand bed test and static bearing test, including film forming agent CY-1, nano-calcium carbonate and nano-silica, and their optimal dosages were determined. Thus, the film plugging drilling fluid system with the density of 1.68 g/cm³ were developed, i.e., bentonite slurry+0.4% KAPM+3% SPNH+3% SMP+2% FT-1+1% PAC-LV+2% CY-1+1% nano-silica+2% nano-calcium carbonate+barite. Finally, its properties were evaluated. It is shown that this drilling fluid system has temperature resistance of 200 ℃, medium pressure fluid loss of 6.8 mL, high temperature and high pressure fluid loss of 8.8 mL and filter cake acid solubility of 24.9%. In conclusion, this physical+chemical film plugging drilling fluid system can solve the problem of gas cut in the process of well drilling in Shunnan Block.